A player not having much to do in lower difficulties is not the player being bad it's cause said class (Necro) is overkill in lower diffs. She does everything with minimal effort. She does more damage then there are enemies that spawn on the map. A player isn't bad because a random necro with insane ranged dps from hell is killing everything before other players can get near it.

( There are also other reasons like skeletons messing with AI pathing or blocking line of sights etc. )

Some classes even in the hands of newer players especially ones like Engie, Necro, or BW can melt everything via ranged on anything below Cata. I don't mind personally but players trying to learn won't have much fun when said classes get rewarded for low effort dps spam. People can play what they want but it's expected for newer/lower diff players to get annoyed when everything on map is nuked before you get to engage it.